Polyphenylene ether (also referred to as polyphenylene oxide or PPO) resins are known in the art as a class of thermoplastics which are characterized by excellent physical properties, including hydrolytic stability, dimensional stability and excellent dielectric properties. In general, they are prepared by the oxidative coupling of a phenolic compound with complex metal catalysts, e.g., a complex copper catalyst. The preparation of polyphenylene ether resins is described in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and U.S. Pat. Nos. 3,257,357 and 3,257,358 of Stamatoff, the teachings of which are incorporated herein by reference.
The high molecular weight polyphenylene ethers are high performance engineering thermoplastics possessing relatively high melt viscosities and softening points, that is, in excess of 250.degree. C., and are useful for many commercial applications requiring high temperature resistance including formation of film, fiber and molded articles.
Cisek, U.S. Pat. No. 3,383,435, which is incorporated herein by reference, discloses polyphenylene ether-styrene resin compositions including rubber-modified styrene resin-polyphenylene ether resins wherein the rubber component is of the unsaturated type such as polymers and copolymers of butadiene. Although the styrene resin component improves the moldability of the polyphenylene ethers, these compositions are still difficult to process. Polyphenylene ether/styrene resin blends comprising between about 25 and 75% of polystyrene units are available commercially from the General Electric Company under the NORYL trademark.
The use of brominated and/or chlorinated compounds by themselves or in combination with other materials such as organic phosphates, boron compounds, etc., as flame retardants for polyphenylene ether resin compositions are well known in the art and are exemplified by U.S. Pat. Nos. 3,257,357; 3,639,506; 3,733,307; 3,809,729; 3,867,336; 3,919,356; 3,936,414; 3,974,235; 3,939,531; 4,024,093; 4,034,136; 4,073,772; 4,094,856; 4,096,117; 4,107,232; 4,191,685; 4,203,931; 4,206,154; 4,274,998; 4,280,951; 4,298,514; 4,301,062; 4,355,126; 4,403,057; 4,446,272; and 4,456,720. The aforesaid patents are incorporated herein by reference.
Further, tetrahalophthalate esters have been used as flame-proofing materials. For example, U.S. Pat. No. 4,098,704 describes the use of these materials as textile finishing agents. U.S. Pat. Nos. 4,298,517 and 4,397,977 disclose these compounds as flame retardants for halogenated resins. However, prior to the inventions of the above related applications of Lovenguth, it was unknown to use these compounds as flame retardants or processing aids for polyphenylene ether resins.
Halogen substituted phthalimides have also been used as flame-proofing materials. For example, U.S. Pat. No. 3,873,567 describes the use of these materials as flame retardants in polymers, etc., especially polypropylene, but also for polyphenylene ether resins and resin blends. U.S. Pat. Nos. 4,087,441 and 4,125,535 describe processes for preparing bis(tetrahalophthalimides) from diaminoalkanes. U.S. Pat. Nos. 3,950,307 and 4,226,989 describe the use of melamine monophthalimides and halobenzoyl phthalimides, respectively, as flame retardants in polymers. U.S. Pat. No. 4,003,862 describes halosubstituted bisphthalimides as flame retardants for polyurethanes, polystyrene and ABS, while U.S. Pat. No. 4,374,220 describes the use of halosubstituted mono-and bis-phthalimides for polyethylene, polypropylene, ethylene-propylene copolymers, etc.
U.S. Pat. No. 4,401,778 describes halogenated imide-containing polyols as flame retardants for polyurethanes as well as other thermoplastic polymers. U.S. Pat. No. 4,320,049 describes halogen-substituted phthalimides containing sulfonic acid groups as their alkali metal salt as flame retardants for polycarbonates. British Pat. Nos. 1,584,202 and 1,584,203 describe the use of N-substituted tetrabromophthalimides as flame retardants for use in polyesters while British Pat. No. 2,114,127 describes carbonate-substituted polyhalophthalimides as flame retardants for polystyrene, ABS and polyethylene.